Coaxial rotary joint



May 17, 1960 F. w. YEAGLEY COAXIAL ROTARY JOINT Filed April 3, 1958INVENTOR F67! M Yewawv 1 y l w ATTORNEYS United States Patent COAXIALROTARY JOINT Frank W. Ye'agley, Dallas, Tex., assignor to ContinentalElectronics Manufacturing Company, Dallas, Tex., a corporation of TexasApplication April '3, 1958, Serial No. 726,174 8 Claims. (Cl. 114-21 Thepresent invention relates to a coaxial cable rotary joint.

Coaxial cables for transmitting radio waves may be required to haverotary joints in order to permit one portion of the cable to rotate withrespect to the other portion. Such rotary joints may be needed, forexample, where the cable is connected to a rotating load, such as arotatable antenna. It is desirable that such rotary joints should makegood contact and prevent leakage of the radio frequency field. The jointshould also by reason of its good contact avoid sparking or coronaeffects. It is desirable that the joint should physically close thecable, so as to prevent contamination thereof. Another desirable featureof a rotatable joint adapted to rotate continuously is that it shallhave minimal wear and a very long life. Still another desirablecharacteristic is a low standing wave ratio.

It is an object of this invention to provide a rotary coaxial cablejoint which has all of the above-mentioned desirable characteristics.

Another object of the invention is to provide a rotary joint which issimple and inexpensive in construction and permits very easy assembly ofthe cable at the joint.

The above and other objects and advantages of my invention will beapparent from the following description and the accompanying drawings,in which:

Fig. 1 is a cross sectional view of one embodiment of my invention;

Fig. 2 is a view of a flat layout of one of the connectors of myinvention; and

Fig. 3 is a view of the outline of the tapered connectors.

Fig. 1 of the drawings shows a coaxial cable rotatably connected to alike coaxial cable 12. These cables may have inner and outer conductors14 and 16 and con ductors 18 and 20. The inner conductors having thesame diameter and the outer conductors having the same diameter. Theouter conductors terminate adjacent each other at 21 and the innerconductors terminate adjacent each other at 22. The conductors arecircular cylinders. Outer conductor 16 is provided with a connector 24conductively fastened thereto in any suitable manner, such as bysoldering indicated at 26. Connector 24 is preferably formed of aresilient metallic material of high conductivity and extends a variabledistance into conductor 14 and is in good conductive contact therewith.A conductor 18 is similarly fastened to a conductor 28 by any suitablemeans such as soldering 30.

The connector 24 is provided with a series of parallel axially extendingslots 32 at one end defining a like plurality of contact fingers 34which are preferably of equal width and substantially equal length.Connector 28 is similarly provided with a regular series of parallelaxially extending slots 36 defining resilient contact fingers 38. Thecontact fingers 34 may have sufficient resilience to provide firmcontact with conductor 14 and fingers 38 of connector 28 may similarlyprovide firm contact with inner conductor 20. If desired, however, thecontact fin- 2,937,224 Patented May 17, 1960 ICC gers may each carry acontact button 40 made of a special material for use as a slidingcontact, such material being chosen for its compatibility with thematerial of the solid conductor upon which it slides. Certain sinteredcontact materials, such as silver and graphite compounds, or tungstenand graphite compounds, are available and useful as contact buttons. Thecontact buttons may be fastened to the contact fingers in any suitablemanner.

A feature of the invention is that each of the connectors terminate in ahelical curve 42 and 44, so that each contact finger extends to adifferent point along the length of the coaxial cable. This staggered,or tapered, or helical arrangement of the contact fingers enables eachindividual finger or contact thereof to have its own contact area on thesolid conductors 14 and 20. Hence, during rotation, each contact willtravel over a different path so that all of the contacts do not Wear asingle annular path around the conductors 14 and 20. This construction,therefore, provides a considerable improvement with regard to the lifeof the rotary joint. Also, the tapered or spiral arrangement of thecontacts provides a more gradual transition from one inner conductor tothe other and from one outer conductor to the other than that would beobtained if all contacts were in the same annular path. Connectors 24and 28 may be formed so that their terminations, as defined by curve 42and 44 extend over a considerable fraction of a wavelength, for thepurpose of producing a gradual transition or junction between theconductors in order to achieve less discontinuity and a smaller standingwave. The connectors having a helical termination have a flat layoutwhich is shown in Figure 2 and may be formed of a single fiat strip ofthe shape shown in Figure 2. The strip 24 or 28 is simply cut on thebias 46 and then suitably slotted to form the contact fingers. Whenrolled up, the connector will then have the desired helical or spiralform, an outline of which is shown in Figure 3.

Although I have shown only on embodiment of my invention, in order tosimply illustrate the principles thereof, it will be evident to thoseskilled in the art that many variations and modifications thereof may bemade within the spirit and scope of my invention as defined in thefollowing claims.

I claim:

1. In combination, first and second connected aligned coaxial radiofrequency transmission lines each having inner and outer cylindricalconductors, one of the outer conductors having an extension telescopedinto the other outer conductor, said extension having a tapered length,one of the inner conductors having an extension surrounding the otherinner conductor and having a tapered length.

2. Apparatus according to claim 1 wherein said conductors have circularcross-sections and said extensions resiliently and rotatively engagesaid other conductors to form a rotatable joint between said first andsecond transmission lines.

'3. A coaxial cable rotary joint comprising a first portion and a secondportion having telescoped first and second inner conductors andtelescoped first and second outer conductors, said first inner and outerconductors each having electrical contacts near the end thereoffrictionally and rotatably engaging said second inner conductor andouter conductor, respectively, the contacts being disposed to makecontact on each of said second conductors at different points along thelength thereof.

4. A rotary joint according to claim 3, wherein the contacts of theinner and outer conductors are arranged helically.

5. A rotary joint according to claim 3, wherein each first conductorincludes a connector formed of resilient material and conductivelyfastened at one end to said first conductor, said connector beingtapered at its other end, said other end being slotted in the axialdirection to form resilient contact fingers engaging the correspondingsecond conductor.

6. A rotary joint according to claim 5, wherein the connector for theouter conductors is therewithin and the connector for the innerconductors surrounds said inner conductors.

7. A rotary joint according to claim 5, wherein the connectors taperover a considerable fraction of a Wavelength of the wave adapted to betransmitted by the coaxial cable.

8. In combination, first and second coaxial high frequency transmissionlines each having inner and outer cylindrical conductors, both innerconductors and both outer conductors being in axial alignment, one ofthe outer conductors being telescoped into the other outer conductor adistance which varies round its circumference, said one outer conductorbeing in contact with the inner wall of the other outer conductor, oneof the inner References Cited in the file of this patent UNITED STATESPATENTS 701,209 Luke May 27, 1902 2,280,728 Streib Apr. 21, 19422,345,019 Van Alstyne Mar. 28, 1944 2,449,073 Johannesen Sept. 14, 19482,822,418 Dinnick Feb, 4, 1958 FOREIGN PATENTS 566,852 Great BritainJan. 17, 1945 579,276 Great Britain July 30, 1946

